fix(desktop): timestamps follow the macOS region and Linux LC_TIME settings

apps/desktop/src/electron/ElectronApp.test.ts

@@ -0,0 +1,89 @@
+import { assert, describe, it } from "@effect/vitest";
+import * as HostProcess from "@t3tools/shared/HostProcess";
+import * as Effect from "effect/Effect";
+import { beforeEach, vi } from "vite-plus/test";
+
+const { getSystemLocaleMock, getUserDefaultMock } = vi.hoisted(() => ({
+  getSystemLocaleMock: vi.fn(() => "en-GB"),
+  getUserDefaultMock: vi.fn((_key: string) => false),
+}));
+
+vi.mock("electron", () => ({
+  app: {
+    getSystemLocale: getSystemLocaleMock,
+  },
+  systemPreferences: {
+    getUserDefault: getUserDefaultMock,
+  },
+}));
+
+import * as ElectronApp from "./ElectronApp.ts";
+
+describe("ElectronApp", () => {
+  beforeEach(() => {
+    getSystemLocaleMock.mockReset();
+    getUserDefaultMock.mockReset();
+  });
+
+  it("keeps the macOS region override and hour cycle in the locale tag", () => {
+    assert.strictEqual(ElectronApp.toSystemLocaleTag("en_GB"), "en-GB");
+    assert.strictEqual(ElectronApp.toSystemLocaleTag("en-US@rg=nlzzzz", "h12"), "en-NL-u-hc-h12");
+    assert.strictEqual(ElectronApp.toSystemLocaleTag("en_US@rg=nlzzzz"), "en-NL");
+    assert.strictEqual(ElectronApp.toSystemLocaleTag("en-GB", "h23"), "en-GB-u-hc-h23");
+  });
+
+  it("drops ICU keywords Intl cannot read instead of losing the whole locale", () => {
+    assert.strictEqual(ElectronApp.toSystemLocaleTag("de_DE@calendar=buddhist"), "de-DE");
+  });
+
+  it.effect("follows LC_TIME on Linux when it differs from the language", () =>
+    Effect.gen(function* () {
+      const electronApp = yield* ElectronApp.ElectronApp;
+      const systemLocale = yield* electronApp.systemLocale.pipe(
+        Effect.provideService(HostProcess.Platform, "linux"),
+        Effect.provideService(HostProcess.Environment, {
+          LANG: "en_US.UTF-8",
+          LC_TIME: "de_DE.UTF-8",
+        }),
+      );
+
+      assert.strictEqual(systemLocale, "de-DE");
+    }).pipe(Effect.provide(ElectronApp.layer)),
+  );
+
+  it.effect("falls back to Chromium's locale on Linux when the time locale is C", () =>
+    Effect.gen(function* () {
+      getSystemLocaleMock.mockImplementationOnce(() => "fr-FR");
+      const electronApp = yield* ElectronApp.ElectronApp;
+      const systemLocale = yield* electronApp.systemLocale.pipe(
+        Effect.provideService(HostProcess.Platform, "linux"),
+        Effect.provideService(HostProcess.Environment, { LANG: "C.UTF-8" }),
+      );
+
+      assert.strictEqual(systemLocale, "fr-FR");
+    }).pipe(Effect.provide(ElectronApp.layer)),
+  );
+});
+
+it.effect("reads both macOS hour preferences without overriding explicit formats", () =>
+  Effect.gen(function* () {
+    for (const [preference, expected] of [
+      ["AppleICUForce12HourTime", "en-NL-u-hc-h12"],
+      ["AppleICUForce24HourTime", "en-NL-u-hc-h23"],
+      ["", "en-NL"],
+    ]) {
+      getSystemLocaleMock.mockReturnValue("en_US@rg=nlzzzz");
+      getUserDefaultMock.mockImplementation((key) => key === preference);
+      const locale = yield* ElectronApp.make.systemLocale.pipe(
+        Effect.provideService(HostProcess.Platform, "darwin"),
+      );
+      assert.strictEqual(locale, expected);
+      for (const hour12 of [true, false]) {
+        assert.strictEqual(
+          new Intl.DateTimeFormat(locale, { hour: "numeric", hour12 }).resolvedOptions().hour12,
+          hour12,
+        );
+      }
+    }
+  }),
+);

apps/desktop/src/electron/ElectronApp.ts

@@ -1,3 +1,4 @@
+import * as HostProcess from "@t3tools/shared/HostProcess";
 import * as Context from "effect/Context";
 import * as Effect from "effect/Effect";
 import * as Layer from "effect/Layer";
@@ -93,6 +94,21 @@ const addScopedAppListener = <Args extends ReadonlyArray<unknown>>(
       }),
   ).pipe(Effect.asVoid);
 
+export function toSystemLocaleTag(identifier: string, hourCycle?: "h12" | "h23"): string {
+  const [base = "", keywords = ""] = identifier.split("@");
+  const languageTag = base.replace(/_/g, "-");
+  // Intl ignores rg extensions, so the macOS region override must replace the region subtag.
+  const region = /(?:^|;)rg=([a-z]{2}|\d{3})zzzz(?:;|$)/i.exec(keywords)?.[1]?.toUpperCase();
+  try {
+    return new Intl.Locale(languageTag, {
+      ...(region ? { region } : {}),
+      ...(hourCycle ? { hourCycle } : {}),
+    }).toString();
+  } catch {
+    return languageTag;
+  }
+}
+
 /** @public */
 export const make = ElectronApp.of({
   metadata: Effect.gen(function* () {
@@ -122,8 +138,23 @@ export const make = ElectronApp.of({
     };
   }),
   name: Effect.sync(() => Electron.app.name),
-  // NSLocale returns en_GB-style tags; Intl requires hyphens.
-  systemLocale: Effect.sync(() => Electron.app.getSystemLocale().replace(/_/g, "-")),
+  systemLocale: Effect.gen(function* () {
+    const platform = yield* HostProcess.Platform;
+    let identifier = Electron.app.getSystemLocale();
+    let hourCycle: "h12" | "h23" | undefined;
+    if (platform === "linux") {
+      const env = yield* HostProcess.Environment;
+      const timeLocale = (env.LC_ALL || env.LC_TIME || env.LANG)?.split(".")[0];
+      if (timeLocale && timeLocale !== "C" && timeLocale !== "POSIX") identifier = timeLocale;
+    } else if (platform === "darwin") {
+      if (Electron.systemPreferences.getUserDefault("AppleICUForce24HourTime", "boolean")) {
+        hourCycle = "h23";
+      } else if (Electron.systemPreferences.getUserDefault("AppleICUForce12HourTime", "boolean")) {
+        hourCycle = "h12";
+      }
+    }
+    return toSystemLocaleTag(identifier, hourCycle);
+  }),
   whenReady: Effect.gen(function* () {
     const isPackaged = Electron.app.isPackaged;
     yield* Effect.tryPromise({